Generally, it is known that crystalline microstructures may be fabricated by forming an epitaxial gallium nitride layer on an α-Al2O3 substrate. Typically, such microstructures include a buffer layer such as aluminum nitride between the gallium nitride and the α-Al2O3 so that the lattice constant mismatch between the gallium nitride layer and the α-Al2O3 substrate materials is reduced.
It is also known that crystalline microstructures may be fabricated without buffer layers when the gallium nitride layer epitaxial layer is formed on a base substrate of silicon carbide, silicon or another material that is compatible with the gallium nitride epitaxy.
Additionally, the formation of SiGe layers by epitaxial growth on flat surfaces is also known.
In order to produce crystalline microstructures that have a deposited epitaxial layer with good crystal quality, the base substrate or carrier must have a smoothly finished surface. Thus, it has been necessary to polish such surfaces to obtain a base substrate having very low surface roughness. The polishing steps necessary to achieve smoothly finished base substrates are time-consuming, costly, and have low efficiency. Moreover, such polishing steps are particularly difficult when materials such as SiC are to be polished. Silicon carbide and other similar materials can only be polished with a very low efficiency due to their thinness and hardness qualities. Thus, such materials are typically provided having an increased surface roughness and defects such as surface scratches. These drawbacks have lead those skilled in the art to the opinion that SiC substrates are not suitable for fabricating high quality heteroepitaxial structures, such as structures with a gallium nitride layer.
Thus, there is a need for a more efficient method for fabricating a microstructure, especially a heteroepitaxial microstructure, with high crystal quality and a high degree of surface smoothness, and to provide a high quality microstructure with a smooth surface which can be fabricated efficiently.